Pyridinium inhibitors for acidizing processes



United States Patent 3,252,980 PYRIDINIUM INHHBITORS FOR ACIDIZING PROCESSES Perce W. Bolmer, Dallas, and Scotty J. Norton, Austin, Tex., assignors to Socony Mobil Oil Company Inc., a corporation of New York No Drawing. Filed Aug. 30, 1962, Ser. No. 220,559 4 Claims. (Cl. 260-290) This invention relates to corrosion inhibitors for inhibiting the corrosion of ferrous metals by mineral acid solutions. More particularly, it is concerned with inhibitors that reduce the corrosion of ferrous metals which occurs during the acidizing of wells.

Acidizing processes, which include the step of injecting mineral acids into well-penetrated formations, are used to a great extent in the petroleum industry. These acidizing processes are generally utilized to stimulate the production of hydrocarbons from the subsurface formations penetrated by such wells.

A variety of acids can be used in such acidizing processes. Generally, a mineral acid is used and usually it is hydrochloric acid because of its efficiency and economy in increasing the permeability of formations penetrated by a production well. The acidizing process includes the step of forcing the acid through the metal conduit contained in the production well and into the desired formation through openings in such conduit adjacent this formation. The acid within the wellbore is held in intimate contact with the formation for a predetermined length of time sufiicient to obtain the desired increase in permeability therein, and then it is removed from the well. Generally, the acid will remain within the well for a period of one to two hours before it is removed. However, for various reasons, the acid may remain within the well for greater lengths of time.

Modern drilling techniques are providing wells into hydrocarbon-containing formations disposed at relatively great depths below the surface of the earth. It is well known that the temperature increases proportionately to the increase in depth of such wells. For example, a well of a depth between 10,000 and 15,000 feet will have a temperature existing adjacent the bottom of the borehole of between 250 F. and 300 F. The temperature of an acid injected into such deep well will vary in temperature between the ambient temperature at the earths surface of about 100 F. to a temperature at the bottom of the well in the range of between 250 F. and 300 F. Severe corrosion to the ferrous metals within such deep well can occur as a result of the duration of contact ofsuch metals with the acid, the temperature of the acid, or both.

It is well known to inhibit the hydrochloric acid used in conventional acidizing processes to reduce the corrosion of Well-contained ferrous metals exposed to such acid. The selection of a proper inhibitor to be added to the acid solution requires careful consideration of the above mentioned conditions encountered in conventional acidizing processes. The inhibitor must be effective throughout the wide range of temperatures encountered in the acidizing process. Also, it must remain effective for a length of time in excess of the normal time interval required for the acidizing process to protect the ferrous metals immersed in such acid solution during an extended period of acidizing.

The known organic inhibitors having suitable characteristics for inhibiting acid solutions have not been found effective in acidizing processes encompassing the above severe conditions for various reasons. One of the One of these reasons is that residual amounts of these inhibitors remain within the well after acidizing and thereafter are removed in minute quantities along with the produced oil. These minute quantities of inhibitors are severe catalyst poisons and therefore the oil must be subjected to expensive treatments before it can be refined in installations involving the use of a catalyst.

It is an object of the present invention to provide organic compounds useful as inhibitors for reducing the corrosion of ferrous metals by mineral acid solutions. It is an object of this invention to provide inhibitors that remain effective in acidizing processes over a wide range of temperatures. An object of this invention is to provide inhibitors for use in acidizing processes that remain effective for a sufiicient length of time to permit normal acidizing operations to be completed in safety. Another object of this invention is to provide inhibitors for use in preventing the corrosion of ferrous metals by mineral acid solutions at temperatures which range from ambient temperatures to as high as 300 F. These and further objects will become more apparent when considered in conjunction with the following detailed description and the appending claims.

In accordance with the present invention, there are provided inhibitors comprising the reaction products of a pyridine compound with an alkylene dihalide Which are useful to inhibit the corrosion of ferrous metals by mineral acid solutions.

The inhibitors of this invention are high-molecular weight bis-quaternary ammonium halide salts, mono-quaternary ammonium halide salts, and mixtures of such salts, all products of the reaction between the above-mentioned reactants.

The pyridine compound and alkylene dihalide will be discussed prior to discussion of their reaction.

The pyridine compound usable in this invention has a pyridine ring as the necessary basic constituent for reaction with an alkylene dihalide. Thus, because of the basic constituent criterion any pyridine ring-containing compound can be used inasmuch as the pyridine ring provides them with a community property. The pyridine compound, as this term is used herein, includes pyridine and the alkylpyridines, as individuals or in mixtures with one another. The pyridine compound may be most easily obtained by the fractionation of coal tar into desired boiling ranges to provide the suitable pyridine ring-containing material. However, it is to be understood that the pyridine compound can be obtained from other sources. Examples of specific embodiments of the pyridine compound include pyridine, methylpyridines, dimethylpyridines, trimethylpyridines, and other alkylpyridines having molecular weights up to about 300. The alkyl radical may comprise one or more hydrocarbon chains carried on the pyridine ring at various ring positions. A readily available pyridine compound is Alkylpyridine HB. Alkylpyridine HE is a commercially available inhibitor and can be used to satisfactorily inhibit mineral acid solutions under conditions less severe than those heretofore set forth. This compound has suflicient alkyl group substitution to the pyridine ring to provide an average molecular weight of about 170. It is a mixture of highboiling alkylpyridines with an equivalent weight of approximately 170 and can be obtained from Carbide and Carbon Chemicals Company.

Inhibitors prepared from a pyridine compound selected from the disclosed community grouping will have sulficient solubility at ambient temperature of about F. to permit an effective amount of such inhibitor to be dissolved in the acid solution. Also, such inhibitors are suiticiently active and also stable at temperatures in the range of between about 250 F. to 300 F. to permit acidizing to be safely carried out for extended periods of time Patented May 24, 1966' at these temperatures. Alkylpyridines having molecular weights in excess of 300 can be used if less desirable results can be tolerated.

The alkylene dihalide usable in this invention also possesses community properties. The alkylene dihalide, as this term is used herein, can be represented by the formula:

In the formula, X is a halide selected from the group consisting of iodine, bromine, and chlorine. The halide is preferably iodine because it is more reactive with the pyridine compounds than the other mentioned halides. In the formula, I: is an integer between 1 and 5. The resistance of the novel inhibitors of the present invention to high-temperature degradation of their efficiency is more pronounced wherein the n is 1. For reasons more apparent from the following disclosure, the preferred alkylene dihalide is methylene iodide. Although the pyridine compound can be reacted with alkyl halides to provide quarternary ammonium salt derivatives, these derivatives, while providing improved inhibitor efliciency, are not as satisfactory as the inhibitors of the present invention.

As previously disclosed, the pyridine compound is reacted with an alkylene dihalide to produce the mentioned inhibitors. Although these reactants will react in any mol-to-mol proportions where the quantity of reactants is suiiicient to react, it is preferred that the pyridine compound is reacted with the alkylene dihalide in mol-to-mol proportions from about 3 to 1 to about 1 to 3. The best results from the inhibitor are obtained with a mol-to-mol proportion of between 3 to 1 to about 1 to 1. Other molar proportions may be used where less than the best results can be tolerated.

The reaction to produce the inhibitors of this invention will now be described. A reaction mixture of the selected pyridine compound and the selected alkylene dihalide is prepared by mixing these materials within the above molar proportions. The reaction mixture is placed into a reaction vessel that is adapted to be heated and from which the escape of vaporous materials is restricted by a watercooled condenser or the like. The reaction mixture is heated to about the reflux temperature to secure a steady reflux in the condenser whereby the desired reaction occurs rapidly at uniform conditions to produce a reaction product having the best inhibitor characteristics. The mixture is heated for a sufiicient length of time until the reaction mixture ceases to increase in viscosity. The reaction is substantially complete under these conditions. It is found that separation of the reaction product from any other materials remaining in the reaction vessel is not required, and, thus, the reaction product can be used as is for the inhibitors of this invention. The reaction of the pyridine compound with the alkylene dihalide is obtained at atmospheric pressure under steady reflux conditions from about 2 to 4 hours. Two hours of steady refluxing is usually suflicient. The rate of reaction may slightly vary depending upon the individual pyridine compound and the alkylene dihalide employed and the concentrations of these reactants.

The reaction conditions of pressure, temperature, and reaction time may be varied to accommodate the physical characteristics of the various reactants under refluxing conditions as is apparent to one skilled in the art.

The inhibitors provided by the reactants undergoing the above reaction are very viscous and may even appear as semicrystalline solids in their purified forms. It has been found that the use of a solvent expedites the handling of the reaction product after it is prepared. Further, it appears that the formation of the novel inhibitors of the present invention is somewhat enhanced through the use of a polar solvent such as methanol. Other polar solvents can be used and it appears that the criterion for their selection is a polar solvent which can effectively solvate a halide ion rather than one which merely has the greatest dielectric constant. However, nonpolar solvents such as benzene can be used.

The inhibitor of the present invention as a reaction product of a pyridine compound with an alkylene dihalide may be represented by the Formulas A and B:

Formula A represents the bis-quaternary ammonium halide salt, and B represents the mono-quaternary ammonium salt. Generally, the inhibitor will consist of mixtures of Formulas A and B. The exact proportion of inhibitors of Formulas A and B in a mixture is dependent upon the molar proportions of the pyridine compound and the alkylene dihalide in a reaction mixture and the conditions of the reaction. However, the inhibitor is equally effective for all practical purposes whether of the form represented by Formula A, or Formula B, or a mixture of Formulas A and B.

In the formulas, y is an integer between 1 and 5, and X represents a halide selected from the group consisting of iodine, bromine, and chlorine. R, in the formulas, in each occurrence, is a material carried on'the pyridine rings and is selected from the group consisting of hydrogen and alkyl radicals. The alkyl radicals contain not more than sufficient carbon atoms to provide the pyridinium compound with a molecular weight not in excess of 300.

The inhibitor in its preferred embodiment may be represented by the Formula A, wherein y is 1, X is iodine, and R, in each occurrence, is an alkyl radical having suflicient carbon atoms to produce an inhibitor having a molecular weight of approximately 600. Such inhibitor is obtained by the reaction of Alkylpyridine HB with methylene iodide in a mol-to-mol-proportion of 2 to 1.

The pyridinium compound referred to in the above formula description is represented by the radical:

and

wherein R is the same material defined in respect to Formulas A and B.

These inhibitors were added to mineral acid solutions in contact with samples of ferrous metals under conditions reasonably reflecting the severe conditions present within a well during normal acidizing processes. There were included tests in mineral acid solutions at a plurality of temperature between F. and 300 F. The results of these tests demonstrated the great utility of the inhibitors of the present invention.

The test utilized was the so-called Carius Technique (Carius, G. L., Ann. d. chem. u. pharm., 136 129 (1865)) in which a solution of inhibitor and acid is heated in a sealed glass vessel containing a sample of ferrous metal. This technique permits accurate and rapid evaluations of inhibitor to be made from the loss of weight of the ferrous sample. Pressure developed within the sealed vessels is due to the vapor pressures of the acid solutions at the test temperature and the pressure of the hydrogen evolved in the corrosion reaction.

The mineral acid solution utilized in all of the tests was 15 percent (by weight) hydrochloric acid which is a mineral acid solution commonly used in acidizing operations. The acid solution wasprepared by diluting four volumes of Dupont Reagent Grade hydrochloric acid (36.5-38.0 percent hydrogen chloride) with six volumes of distilled water.

The ferrous samples exposed for weight loss in all of the tests were four-inch-long cylindrical pieces of No. 20 iron wire having a diameter of approximately 35 mils. The wires were cleaned by immersing them first in acetone and then in 15 percent hydrochloric acid. Thereafter, they were rinsed first with water and then with acetone. The wires were air dried and weighted immediately before use.

The wire were placed into individual glass vessels made of round-bottom tubes. Each of the tubes formed a chamber in which 30 milliliters of acid solution would completely cover the contained iron wire. The glass vessels had a constricted top portion such that the vessel could conveniently be closed by use of a gas-oxygen flame on the constriction to provide a vapor-proof seal. The sealed vessels were placed into a heat sink and heated uniformly to the desired temperature of between 120 F. and 300 F. for the desired time interval. After heating, the vessels were removed from the sink and opened by breaking. The iron wires were removed, rinsed first with water and then with acetone. They were air dried and weighed.

Since the iron wires were cylindrical, surface corrosion penetration during exposure to the acid was not directly proportional to the weight loss of the sample. This is due to the fact that penetration of the circular cross section reduced the radius of the cylinder while the weight loss depended on a volume decrease. Thus, a squareroot relationship exists between the radius reduction and weight loss.

Assuming uniform corrosion with no pits or areas of concentrated attack, the following equation for penetration during an exposure period was derived:

Penetration rate (mils per hour) Exposure time (hours) (1) In Equation 1: r =Radius of wire before test (17.5 mils), and

ts areas: due weight loss: X (100) Weight of wire before test Utilizing the above test procedure and calculations it was found that at 300 F. the penetration rate of the uninhibited hydrochloric acid solution (in mils per hour -hereinafter abbreviated m.p.h.) was 94 m.p.h. This is over thirty times the minimum safe rate and is over ten times the rate at 200 F. The rate at 120 F. was .24 mph, at 163 F. was 1.9 mph, at 192 F. was 7.0 mph, at 200 F. was 8 mph, at'250 F. was 22 m.p.h., and at 275 F. was 54 mph The following examples will be further illustrative of the invention.

Example 1 A reaction mixture was prepared by mixing 50 milliliters of Alkylpyridine HB and 10 milliliters of methylene iodide in a round-bottom flask. To the reaction mixture was added milliliters of methanol as a solvent. The mol-to-mol proportion of the Alkylpyridine HB to the methylene iodide in such reaction mixture is 2.35 to 1. The mixture was heated sufficiently to secure a steady reflux in the condenser at atmospheric pressure. The mixture was heated at a steady reflux until the reaction mixture products ceased to increase in viscosity. The reaction product in the flask was used in the Carius Technique tests at 300 F. without further treatment and in a concentration of one percent by volume in the mineral acid solution. The Alkylpyridine HB, a com- The results of the Examples 2 t0 7 In the Table I following, there are set forth results of tests at temperatures other than 300 F. for the reaction product of Alkylpyridine HB with methylene iodide, prepared and tested, as was the inhibitor of Example I. Alkylpyridine HE is provided for comparison purposes at each listed temperature.

Examples 8 to 10 Various alkylpyridines were reacted with methylene iodide in the manner of Alkylpyridine HB and tested for effectiveness at 163 F. The results of these tests are set forth in Table I.

TABLE I Inhibitor (All percentages on Tempera- Exposure Penetravolume-to-volume base) ture F.) (Hours) tion Rate (m.p.h.)

Example 1:

I 1 (1%)- 300 2 8.7 II 2 (1%). 300 4 1. 2 Examples 2 to 7:

(1%) 275 4% 1.9 II (1%) 275 22 0. 54 I (l%) 250 15 0.50 II (1%) 250 15 0.14 I (2%) 225 4%) 0. 04 II (1%). 223 5 0. 04 I (2%)." 192 4910 0. 04 II (1%) 192 18% 01 (2%) 163 4%0 02 II (1% 163 18% 01 (1%) 4%0 0. 01 II (1%) 120 18% 01 Examples 8 to 10:

Pyridine plus methylene iodide product (2%) 163 19% 0. 02 2, 3, Lutidine plus methylene iodide product (2%) 163 18% 0. 02 2, 4, 6, trimethylpyridine plus methylene iodide product (06%) 163 19% 0.02

l Inhibitor I is Alkylpyridine HB. Inhibitor II is the reaction product of Alkylpyridine HB with methylene iodide.

It was found that the inhibitors herein disclosed were satisfactory for inhibiting mineral acid solutions during normal acidizing processes when used in an amount of about 0.05 percent by volume of the acid solution. At temperatures of 300 F., 1 percent by volume of the inhibitor in the acid solution was highly effective. Greater concentrations of the inhibitors can be used if desired to more fully retard the corrosive attack on ferrous metals by the immersing mineral acid.

It appears that the presence of iodide, as an ion or in a nonionic form, in the acid solution in many cases may enhance the effectiveness of the inhibitors of the present invention. The degradation of the monoor bis-quaternary ammonium salts, according to one theory, would result in some quantity of an acid, the hydrogen halide, being released into the acid solution. Thus, even though a portion of the inhibitor might be decomposed at elevated temperatures, the hydrogen halide provides sufficient halide ions, preferably iodide, in the acid solution to enhance the remaining inhibitor sufiiciently to preserve the over-all effectiveness thereof. This, of course, is another advantage of the inhibitors of the present invention. It is believed that the l-alkyl pyridinium salts decompose at high temperature by a loss of hydrogen halide and the migration of the alkyl group from the ring nitrogen to the 2- or 4-ring positions. Thus, a highly alkyl radical-substituted pyridine ring especially with the 2- and 4-ring positions block by alkyl radicals increases the stability of the inhibitors at high temperatures. -Another theory resides in the halide being nonionic. Thus, it is possible that the halide migrates to the pyridine ring to form l-alkyl pyridinium halide complex. However, we do not wish to be limited by the expressed theories regarding the mechanisms by which the inhibitors of this invention achieve their great inhibiting efiiciency, especially at high temperatures. The results in Table I will '7 illustrate the utility of the inhibitors of the present invention.

The inhibitors are added directly to the mineral acid solutions used in the acidizing processes in a well and in the amounts previously set forth. It is preferable to intermix the inhibitors with the acid prior to initiation of the acidizing process but the inhibitors can be added at any step in the acidizing process. Further, the inhibitors can be added to the acid solution at one time in the desired amount or in incremental amounts over a period of time. However, the best results are obtained when the inhibitors are added to the acid immediately preceding the injection of the acid into a wellbore. In this manner, the inhibitors reduce the rate of corrosion of the mineral acid solution from the initiation of the acidizing process.

From the foregoing it will be apparent that there has been disclosed herein inhibitors that are Well suited to be added to mineral acids to prevent corrosion of ferrous metals at temperatures as high as 300 F. Furthermore, these inhibitors are effective in preventing corrosion for a suflicient length of time that normal acidizing processes can be completed in safety. The inhibitors disclosed herein and their use in acidizing processes to inhibit the corrosion of ferrous materials by mineral acids achieve all of the stated objects of the present invention.

While illustrative embodiments of the present invention have been fully described, it will be understood that various changes may be made by those skilled in the art without departing from the spirit of the invention.

The utility of the corrosion inhibitors and processes utilizing the same has been described, as a means of illustration, in conjunction with acidizing processes. However, the utility of the present invention is not limited solely to acidizing processes but can be used to great advantage in other processes wherein mineral acid solutions immerse ferrous metals. An example of such other use is in the injection of mineral acids into Wells to increase the permeability of the formations surrounding the same so that fluids injected into such wells can flow more easily into the formation. Such processes are used to prepare water injection wells for secondary recovery processes so that formation fluids can be recovered from the formation thrtliugh production wells disposed about the injection wel s.

8 What is claimed is: 1. A composition consisting of at least one compound selected from the group consisting of and mixtures thereof; wherein R, in each occurrence, is alkyl, and contains sufiicient atoms so that each substituted pyridyl moiety has an equivalent molecular weight of at least about 170, y is an integer from 1 to 5 inclusive, and X is a halogen selected from the group consisting of iodine, bromine, and chlorine.

2. A composition according to claim 1 wherein X is iodine.

3. A composition according to claim 1, comprising a compound of the Formula A having a molecular weight of approximately 600.

4. A composition according to claim 3, wherein X is iodine, and y is 1.

References Cited by the. Examiner UNITED STATES PATENTS 2,271,378 1/1942 Searle 260290 X 2,446,796 8/1948 Van Campen et al. 167-33 2,814,593 11/1957 Beiswanger et al. 2528.55 2,889,329 6/1959 Luvisi 260290 2,955,083 10/1960 Levin 2528.55 2,995,558 8/1961 Mahan et al. 260--290 OTHER REFERENCES Baer et al.: J. Am. Chem. Soc., vol. 18 (1896), pp. 988-989.

Hartwell et al.: J. Am. Chem. Soc., vol. 72 (1950), pp. 20404044.

Krohnke: Chemische Berichte, vol. 88 (1955), pp. 85l862.

WALTER A. MODANCE, Primary Examiner.

J. GREENWALD, JOHN D. RANDOLPH, Examiners. 

1. A COMPOSITION CONSISTING OF AT LEAST ONE COMPOUND SELECTED FROMTHE GROUP CONSISTING OF 